For oil and condensate fields the pressure out from the well can be too low for effective processing, particularly toward tail production. In order to dump or reinject water separated out from the production flow, the oil contents must be reduced to a sufficiently low level. A pump can be required upstream of hydrocyclones or other separation equipment, in order to provide sufficient inlet pressure to the separator.
A problem not given much attention is that a pump can break up dispersed oil droplets to a size not feasible for effective separation in downstream separation equipment, thereby reducing the efficiency of the separation. Instead of considering the pump design in order to solve the problem, inserting a coalescer or injecting chemicals upstream the separator have been typical solutions.
A remote technical field for which low shear pumping is crucial, is the pumping of blood. However, the pressure and flow rates are not comparable or feasible for pressure boosting of oil, condensate, water or mixtures thereof.
The food industry comprises several processes for which low shear is feasible, for example pumping or transport of milk, other dairy products and emulsions. However, the pressure and flow rates typical for the food industry, for which the pumping is for short distance transport, make pumps for dairies and other food industry pumps unfeasible for pressure boosting of oil, condensate, water or mixtures thereof.
The objective of the present invention is to provide a pump able to provide coalescing effect, low droplet break up of a dispersed phase in a continuous phase, and relative high pressure boosting and high flow rate at the same time.
A number of more or less relevant prior art patent documents have been identified, namely: US 2003007871 A1, CA 2083069 A1, AT 394136 B, GB 1520482 A and U.S. Pat. No. 3,643,516 A. The above mentioned publications describe single stage pumps only, with one impeller or pumping stage. However, for some embodiments, the shape or design of the single impeller is adapted so as to provide low shear. Coalescing pumps are apparently not described.
No pumps having several stages or impellers with particular design of the last or successive impellers or stages so as to provide coalescing effect, low droplet break up, high pressure boosting and high flow rate at the same time have been identified. Multi stage pumps are traditionally made with identical impeller stages or stages that increase the pressure boosting but also the shear in the direction of flow, such as described in patent publication U.S. Pat. No. 7,150,600 B1, contrary to the teaching of the present invention.